The present invention relates to a flame-retardant olefin polymer composition superior in heat resistance and mechanical strength, the olefin polymer composition consisting principally of a copolymer of ethylene and a carboxyl-containing monomer or a derivative thereof and an olefin polymer modified with an unsaturated carboxylic acid or a derivatve thereof.
Polyethylenes are general-purpose resins in greatest demand which are superior in physical and chemical properties and so formed into films, sheets, pipes, containers, etc. according to various methods, including extrusion, injection molding and rotational molding, and are applied to various domestic and industrial applications.
Since those polyethylenes are easy to burn, various methods have heretofore been proposed for rendering them flame-retardant. Among them, the most general method is to add a flame retardant containing halogen or phosphorus to the polyethylenes. The degree of flame retardance increases with increase in the amount of the flame retardant added. However, the increase in the amount of the flame retardant used not only causes deterioration of the mechanical strength and processability but also impairs the flexibility and cold resistance markedly. Further, from the standpoint of fire prevention, conventional flame-retardant compositions are required to be rendered highly flame-retardant and in some regions there is the recent tendency that such high degree of flame retardancy is obligated. Under the circumstances, inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide, which do not evolve a noxious gas during combustion and are low smoking and pollution-free, meet the above needs and are rapidly increasing in demand. (Related techniques are disclosed, for example, in Japanese Patent Laid Open Nos. 132254/1976, 136832/1981 and 13832/1985.)
In the conventional commercial polyethylenes, the acceptability of inorganic flame retardants is poor and the flame retarding effect is low. Besides, with increase in the amount of loading, the mechanical strength as well as flexibility and processability deteriorate to an impractical extent.
On the other hand, the use of non-rigid plastics such as ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, chlorinated polyethylene, or ethylene-propylene copolymer rubber, is well known for increasing the percentage loading of such inorganic flame retardants. But it is inferior in point of mechanical strength and heat resistance.